The extracellular matrix (ECM) is critical for cellular decision-making through its role in tissue architecture and its stimulatory effects on cell growth, migration, and differentiation. Transmission of ECM signals is carried out by integrin receptors that link the ECM to the actin cytoskeleton and activate various signaling pathways. To understand how cells coordinate extracellular signals with intracellular processes requires insights into the composition and organization of the ECM as well as information about the intracellular molecules that respond to cell-ECM interactions. We are approaching these questions by analyzing gonadogenesis in the nematode Caenorhabditis elegans. Formation of the C. elegans hermaphrodite gonad occurs after hatching and depends on migration of two distal tip cells (DTCs) along the body wall basement membrane matrix. In a genome-wide screen, we identified 99 genes that are required for this process. Here we will focus on several of those genes that play critical roles in initiation of DTC migration and in DTC turning to form the U- shaped gonad arms. Loss of the conserved basement membrane protein papilin (ppn-1) causes a complete blockade of DTC migration. Tissue distribution, timing and regulation of expression, rescue of mutants, and expression of protein domains will be used to define papilin's role in gonad formation. Complementary in vitro studies of papilin localization and function will be performed using human mammary epithelial cells which also express this gene. To determine how DTCs interact with basement membranes, we will identify the ECM ligands for the C. elegans integrin receptors that mediate migration. The ECM directs cell turning and accompanying changes in cell polarity, processes that are dependent on two novel genes and on expression of the pat-2 integrin during gonadogenesis. Functional analyses of these genes and time-lapse video microscopy of migrating DTCs will define molecular requirements for turning. Results from these aims will provide novel information about the regulatory role of cell-ECM interactions in cell rearrangements and migration during tissue morphogenesis. Public Health Relevance: Progression of most, if not all, human diseases is facilitated by perturbations in the extracellular matrix, the network of proteins and carbohydrates that surrounds cells. The extracellular matrix plays essential roles in organizing cells into tissues and controlling organ function. The proposed studies will provide novel information about how changes in cell connections to the extracellular matrix affect organ development and will provide new ideas about how alterations in extracellular matrix contribute to human disease.